Pneumatic radial tire with load bearing rubber reinforcing layer

ABSTRACT

A radial pneumatic tire having excellent run-flat durability. The tire is equipped with a belt (4), which includes a plurality of metal cord layers, and a tread (5) successively placed at a periphery of a crown portion (3) of a toroidal radial carcass (2), and is equipped with, at an inner peripheral surface of the side portion (6) of the carcass, a rubber reinforcing layer (7) having a crescent moon shaped cross-section and bearing and supporting load. The tire has an auxiliary belt (8) disposed between the carcass and the belt and including organic fiber cords which are oriented substantially cross to the cords of the carcass and the cords of the belt with respect to a central equatorial plane, the cords of the auxiliary belt substantially crossing the central equatorial plane.

TECHNICAL FIELD

The present invention relates to a pneumatic radial tire, and morespecifically, to a pneumatic radial tire which is strengthened byproviding, at the sidewall of the tire, a rubber reinforcing layerhaving a crescent moon shaped cross-section, such that when thepneumatic tire installed on a vehicle is punctured during running, thetire can run for a considerable distance in the punctured state.

BACKGROUND ART

Conventionally, various measures have been devised for safely continuingrunning, without damaging the tire further and without disadvantagessuch as poor steering. This occurs over a distance from the place wherethe tire was punctured to a place desired by the driver, e.g., a servicestation where the tire can be changed, at the time when the internalpressure decreases or becomes zero (hereinafter, "punctured") for somereason, and in many cases, due to a foreign object such as a nail or ametal piece piercing the tire, during traveling of the pneumatic tireinstalled on a vehicle.

Among these measures, as a simple and effective measure for radial tiresfor passenger vehicles in particular, Japanese Patent ApplicationPublication No. 52-41521 discloses art relating to a so-called sidereinforced run-flat tire in which a rubber reinforcing layer having acrescent moon shaped crosssection is made to line the carcass innerperipheral surface of the sidewall, which is the region in the tirehaving the lowest rigidity, so that the entire sidewall hasapproximately the same thickness and so as to provide rigidity.

In this side reinforced run-flat tire, in an ordinary state, the load ismainly supported by internal pressure. When the tire is punctured, thesupporting of the load is taken over by the rigidity inherent in thereinforced sidewall.

However, in this side reinforced run-flat tire, as illustrated in FIG.2, when the tire is punctured, buckling of a sidewall S is avoided, buta crown portion 21 exhibits the phenomenon known as buckling, and atread 22 is thereby lifted up from a road surface R. As a result, aportion 23 of the sidewall separated from the tread 22 contacts theground.

In this ground-contacting state, obviously, stress concentrates anddefects arise at an early stage at portions at which there is muchbending deformation. As a result, in order to increase the durability ofthe run-flat tire, buckling of the crown portion 21 must be suppressed,and tire deformation must, as much as possible, be maintained the sameas before the puncture.

Japanese Patent Application Laid-Open No. 6-191243 and Japanese PatentApplication Laid-Open No. 6-191244 disclose techniques in which at leastone organic fiber cord layer, which is effective for weight reduction,is disposed at the outer periphery of the belt layer, so as to increasethe rigidity of the tread base portion.

However, these disclosed techniques do not exhibit sufficient effectsfor suppressing buckling, and the current situation is that, even if therigidity of the tread base portion is increased even more, by winding aplurality of layers, the effects are small in proportion to the increasein cost and in weight.

DISCLOSURE OF THE INVENTION

The present invention has taken into consideration the above-describedproblematic points, and an object thereof is to provide a pneumatic tirein which, when the tire is punctured, buckling of the crown portion issuppressed, and durability is increased.

The present invention is a pneumatic radial tire equipped with a belt,which includes a plurality of metal cord layers, and a treadsuccessively placed on a crown portion periphery of a toroidal radialcarcass, and equipped with, at a side portion inner peripheral surfaceof the carcass, a rubber reinforcing layer having a crescent moon shapedcross-section and bearing and supporting load, comprising: an auxiliarybelt disposed between the carcass and the belt and including organicfiber cords which are oriented to substatially cross the cords of thecarcass and the cords of the belt with respect to a central equatorialplane, the cords of the auxiliary belt substantially crossing thecentral equatorial plane

As is known, a belt for improving the rigidity of the base portion ofthe tread is provided at the crown portion of a radial tire. The belt isusually formed by a plurality of steel cord layers. It is known thatwhen, due to a puncture, the tread receives bending deformation to riseup, the steel cord belt becomes a neutral axis, a compressive force isapplied to the tread and tension is applied to the carcass.

Accordingly, in a conventional reinforcing method in which the outerperiphery of the belt is additionally reinforced, the compression sideis reinforced, and the intrinsic tensile direction high elasticity ofthe reinforcing cord is not generated.

The present invention is equipped with an auxiliary belt at the side ofthe crown portion of the tire to which side tension is applied at thetime of a puncture. Accordingly, even if the cords are reinforced byflexible organic fibers, the crown portion is effectively provided withflexural rigidity, and rising up of the tread at the time of a puncturecan be effectively suppressed. As a result, local concentration ofstress can be avoided, and the run-flat running can be greatly improved.In this case, it is preferable that the cords of the auxiliary beltcross the central equatorial plane at an angle of greater than or equalto 30°, because at angles of less than 30° with respect to the centralequatorial plane, sufficient tire radial direction rigidity cannot beobtained and buckling cannot be suppressed. It is even more preferablethat the cords of the auxiliary belt are in a range of 45° to 75° withrespect to the central equatorial plane. It has been confirmed that, inorder to sufficiently and effectively suppress buckling, there must besufficient tire radial direction rigidity, and circumferential directionrigidity must be maintained, and the angle with respect to theequatorial plane is optimally in a range of 45° to 75°.

Other than aramid, polyester, rayon, and the like can be optimally usedfor the organic fiber cords. Further, the number of organic fiber cordlayers is not limited to one, and plural layers may be superimposed suchthat the cords thereof cross each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a tire cross-sectional view of an embodiment to which thepresent invention is applied.

FIG. 2 is a cross-sectional contour view illustrating deformation at thetime a tire is punctured in accordance with a conventional art.

PREFERABLE EMBODIMENT FOR IMPLEMENTING THE INVENTION

In order to confirm the effects of a tire to which the present inventionwas applied, run-flat durability due to actual running on a vehicle wasevaluated for 205/65R15 size Example tires and Conventional Exampletires.

For the test method, each test tire was assembled to a 15×51/2J rim.After internal pressure was filled so that the bead fit the rim, thevalve core was removed, and the test tires having an internal pressureof substantially zero were respectively installed on the front rightwheel of a passenger vehicle. The tires were run on a test track at aconstant speed of 20 km/h. The driver sensed the generation of abnormalvibrations caused by a defect of the test tire (the limit ofdurability), and the running distance until the defect was generated wasmeasured.

EXAMPLE 1

Hereinafter, a description will be given on the basis of the drawing.FIG. 1 is a cross-sectional view of a tire illustrating an embodiment ofthe present invention.

FIG. 1 is an example of a 205/65R15 size passenger vehicle tire (1). Acarcass 2 is formed from two plies in which 1000d/2 polyester cords aredisposed so as to be oriented substantially orthogonally to anequatorial plane O. Both end portions of the carcass 2 are wound uparound bead rings 9 so as to form wound-up end portions 2'. A hardrubber bead filler 10 is embedded taperingly between the carcass 2 abovethe bead ring and the ply wound-up end portion 2' thereof.

At a side portion 6 inner peripheral surface of the carcass 2, a rubberreinforcing layer 7 (Shore A hardness 84°, maximum width 10 mm) having acrescent moon shaped cross-section is disposed such that the entiresidewall S has a substantially uniform thickness from the position wherethe rubber reinforcing layer 7 is superposed on the bead filler via thecarcass. Reference numeral 5 is a tread and reference numeral 11 is anair-impermeable inner liner.

A belt 4 comprises two layers, each layer being a structure in which 1×5twisted steel cords are disposed to be inclined at an angle of 26° withrespect to the equatorial plane O, and the two layers are superimposedsuch that the cords cross one another. An auxiliary belt 8 which isnarrower than the belt is disposed between the belt 4 and the crownportions 3 of the carcass 2.

In Example 1, the auxiliary belt 8 is disposed between the carcass 2 andthe belt 4 and comprises organic fiber cords which are oriented tosubstantially cross the cords of the carcass and the cords of the beltwith respect to the central equatorial plane O. The auxiliary belt 8 isformed by one rubber-coated layer in which 1670d/2 aramid cords aredisposed at an angle of 20° with respect to the equatorial plane O.

The belt may be a structure strengthened by a cap belt which is formedfor example by lining up a plurality of heat shrinking cords such asnylon or the like in a rubber coated strip and winding the cordsspirally in the peripheral direction at the entire periphery or apredetermined region of the periphery of the belt layer.

Although the details of the half at the right side of the equatorialplane O are omitted from FIG. 1, there is symmetry to the left and theright.

EXAMPLE 2

In Example 2, the auxiliary belt 8 of Example 1 is formed from onerubber-coated layer in which aramid cords are disposed at an angle of30° with respect to the equatorial plane O. Example 2 is substantiallysimilar to Example 1 in all other respects.

EXAMPLE 3

In Example 3, the auxiliary belt 8 of Example 1 is formed from onerubber-coated layer in which aramid cords are disposed at an angle of45° with respect to the equatorial plane O. Example 3 is substantiallysimilar to Example 1 in all other respects.

EXAMPLE 4

In Example 4, the auxiliary belt 8 of Example 1 is formed from onerubber-coated layer in which aramid cords are disposed at an angle of60° with respect to the equatorial plane O. Example 4 is substantiallysimilar to Example 1 in all other respects.

EXAMPLE 5

In Example 5, the auxiliary belt 8 of Example 1 is formed from onerubber-coated layer in which aramid cords are disposed at an angle of75° with respect to the equatorial plane O. Example 5 is substantiallysimilar to Example 1 in all other respects.

EXAMPLE 6

In Example 6, the auxiliary belt 8 of Example 1 is formed from onerubber-coated layer in which aramide cords are disposed at an angle of90° with respect to the equatorial plane O. Example 6 is substantiallysimilar to Example 1 in all other respects.

COMPARATIVE EXAMPLE 1

In Comparative Example 1, one layer of the same structure as theauxiliary belt 8 is disposed between the belt and the tread. Theauxiliary belt 8 is formed from one rubber-coated layer in which aramidcords are disposed at an angle of 60° with respect to the equatorialplane O. Comparative Example 1 is substantially similar to Example 1 inall other respects.

COMPARATIVE EXAMPLE 2

Comparative Example 2 is substantially similar to Example 1 except thatno additional cord layer such as the auxiliary belt 8 is used.

The results of measurement of the running distances until defectsoccurred are listed in the following table.

    ______________________________________                                     Comparative                     Examples        Examples                     1     2   3   4   5   6   1       2    ______________________________________    Organic Exists?  Yes             Yes     No    Fiber   Placed   Between carcass and belt                                     Between belt                                             --    Auxiliary                        and tread    Belt    Number of                     1 layer         1 layer --            Layers            Angle    20°                           30°                               45°                                   60°                                       75°                                           90°                                               60°                                                       --    Running Distance until                 5     7     10  15  12  9   3       2    Defect (km)    ______________________________________

In this way, run-flat durability can be advantageously improved byplacing between the carcass and the belt an auxiliary belt includingorganic fiber cords which are oriented to substantially cross the cordsof the carcass and the cords of the belt with respect to the centralequatorial plane the cords of the auxiliary belt substantially crossingthe central equatorial plane, in a tire having, at the side portioninner peripheral surface of the radial carcass, a rubber reinforcinglayer which has a crescent moon shaped cross-section and bears andsupports the load.

PRACTICAL USE OF THE INVENTION IN THE INDUSTRY

As described above, the pneumatic radial tire relating to the presentinvention is useful for use as a tire for a vehicle, and in particular,the pneumatic radial tire which can run for a long distance even ifpunctured is extremely useful to the automotive industry in today'svehicle-oriented society.

I claim:
 1. A pneumatic radial tire comprising; a toroidal radialcarcass, a pair of sidewalls, a belt which includes a plurality of metalcord layers and a tread successively placed on a crown portion peripheryof said toroidal radial carcass, at each side portion inner peripheralsurface of the carcass a rubber reinforcing layer having a crescent moonshaped cross-section and bearing and supporting load, and an auxiliarybelt disposed between the toroidal radial carcass and the belt andincluding organic fiber cords, said cords oriented to substantiallycross the radial cords of the carcass and the cords of the belt withrespect to a central equatorial plane, the cords of the auxiliary beltsubstantially crossing the central equatorial plane.
 2. A pneumaticradial tire according to claim 1, wherein the cords of said auxiliarybelt cross the central equatorial plane at an angle of greater than orequal to 30°.
 3. A pneumatic radial tire according to claim 1, whereinsaid rubber reinforcing layers each have a cross-sectional shape suchthat both sidewalls of said tire have a substantially uniform thickness.4. A pneumatic radial tire according to claim 1, wherein said auxiliarybelt is a single layer of rubber coated aramid cords.
 5. A pneumaticradial tire according to claim 1 further comprising a cap beltpositioned radially outside said belt.
 6. A pneumatic radial tireaccording to claim 5, wherein said cap belt is formed by winding aplurality of heat shrinking cords in a rubber coated strip spirally inthe peripheral direction at the entire periphery or a predeterminedregion of the periphery of the belt.
 7. A pneumatic radial tireaccording to claim 1, wherein said auxiliary belt has a width narrowerthan that of said belt.